Chafing behaviour of great barracudas on sea turtles triggers escape response of external parasites

If chafing behaviours on the bottom or rocks are common, interspecific events are rare and usually involve smaller ray-finned fishes rubbing on larger sharks or manta rays. Reports on interspecific chafing between fishes and reptiles are even less common, with just one report of great barracudas (Sphyraena barracuda) using swimming hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) as chafing surfaces in Southwestern Atlantic. Here we describe a chafing interaction between a great barracuda and a hawksbill turtle in the Red Sea. Our observation provides evidence that this interaction is probably not localised but may represent a more widespread behavioural pattern than previously thought. This chafing behaviour is suggested to remove external parasites, and our observation documents the behaviour of the scraper and the scraped animal, as well as the reaction of the parasites during the same event, clearly demonstrating that chafing behaviour aims at the removal of parasitic copepods (Caligidae). We also report the evasive behaviour of the copepods during the event, providing novel information on parasite removal in reef fishes.